The present invention relates to a process for preparing relief images, and more especially to such a process in which a light-sensitive material composed of a support and a light-sensitive layer is imagewise irradiated and the non-image areas are washed out with a developer liquid. The light-sensitive layer contains as essential constituents
(a) a compound which has at least one C--O--C bond which is cleavable by acid, PA1 (b) a compound which forms a strong acid on irradiation, and PA1 (c) a binder which is insoluble in water and soluble in aqueous-alkaline solutions.
Processes of the generic type mentioned and the light-sensitive materials used in these processes are known. These materials produce positive copies of the exposure original, i.e., the layer becomes soluble in a developer at the exposed areas. Such positive-working materials are described in U.S. Pat. Nos. 3,779,778, 4,101,323, 4,189,323, 4,247,611, 4,250,247, 4,248,957 and 4,311,782. On exposure of these materials, compound (b) forms an acid by photolysis, and the acid cleaves the C--O--C groups of compound (a), so that as a result, the exposed areas of the light-sensitive layers become soluble in a developer.
It is also known to apply a certain sequence of treatment steps in order to process in a negative manner a positive-working reproduction material based on 1,2-naphthoquinonediazides. U.S. Pat. No. 3,264,104 describes such a reverse process, in which the light-sensitive layer, which preferably contains thermoplastic polymers, is imagewise exposed, treated with an alkaline solution or with hot water, without washing out the exposed areas, then re-exposed without the original and subsequently developed in the customary manner. In the developing procedure, the originally imagewise exposed areas are left intact, while the remaining areas are washed out.
A similar process is described in U.S. Pat. No. 3,406,065. In this process also, a layer of the same type is imagewise exposed, treated with aqueous alkali without washing out the exposed areas, then treated with an alkali-resistant lacquer and developed by washing out those areas not imagewise exposed. The developing can be effected either with organic solvents or with aqueous-alkaline solutions, the case where the layer was exposed without the original after the first alkali treatment and before the lacquering.
These processes have the disadvantages (1) that they require a relatively large number of treatment steps, (2) that the first alkali treatment must always be carried out with particular care in order to release as little as possible of the exposed layer, which is soluble in aqueous alkali, (3) that they require the addition of polymers which are sparingly soluble in alkali and restrict the utilizability of the material for other purposes, or (4) that they also require lacquering of the expose layer. Any material based on 1,2-naphthoquinonediazides has the disadvantage in principle of a relatively low light sensitivity.
European patent application No. 24,916 discloses a similar reverse process, in which a material based on 1,2-quinonediazides is heated after imagewise exposure, then re-exposed without the original and developed by means of aqueous alkali to give a negative. The material contains in the light-sensitive layer certain photochromic compounds which react during heating with the light reaction products of quinonediazide and which are said to lead to a hardening of the layer. This material requires the presence of photochromic substances, the light reaction of which produces a discoloration which is troublesome in some applications. It also has the low light sensitivity characteristic of 1,2-quinonediazides.